Table 3.

Median and ranges of differences between the original pCT and the CBCT DVHs for primary (PTV70) and nodal (PTV56) planning target volumes, together with spinal cord and brain stem as OARs (head and neck patients)

Target & OAR	Constraint	Standard pCT calibration curve	CBCT site-specific calibration curve	HU density override	Deformable registration
		Median difference (min; max)	Median difference (min; max)	Median difference (min;max)	Median difference
PTV70	Dose to 99%	−0.4	−0.1	0.1	0.0
	of the volume [%]	(−0.8; 0.3)	(−0.2; 0.5)	(0.0; 0.3)	(−0.2; 0.2)
	Dose to 95%	−0.4	0.0	0.1	0.0
	of the volume [%]	(−0.6; 0.4)	(−0.2; 0.7)	(0.0; 0.3)	(0.0; 0.4)
	Max dose to 1%	0.1	0.7	0.4	0.1
	of the volume [%]	(−0.1; 1.0)	(0.2; 1.3)	(0.3; 1.0)	(0.0; 0.9)
PTV56	Dose to 99%	−1.3	−1.5	−1.2	−2.0
	of the volume [%]	(−5.4; −0.9)	(−3.9; −0.3)	(−3.2; −0.1)	(−2.7; −0.2)
	Dose to 95%	−0.2	0.0	−0.2	−0.4
	of the volume [%]	(−1.1; 0.0)	(0.5; 0.3)	(−0.3; 0.3)	(−0.5; −0.1)
	Max dose to 1%	0.2	0.5	0.5	0.2
	of the volume [%]	(−0.2; 0.7)	(0.1; 1.3)	(0.3; 0.7)	(0.0; 0.7)
Spinal cord	Dose to 0.1 cm3	−0.2	0.0	0.0	0.0
	of volume [Gy]	(−0.4; 0.1)	(−0.1; 0.2)	(−0.1; 0.1)	(0.0; 0.1)
Brain stem	Dose to 0.1 cm3	−0.1	0.2	0.2	−0.1
	of the volume [Gy]	(−0.2; 0.4)	(0.1; 0.5)	(0.0; 0.3)	(−0.3; 0.1)

CBCT, cone beam CT; DVH, dose volume histogram; HU, Hounsfield unit; OAR, organ at risk; PTV, planning target volume.